This invention relates to apparatus and method for cooling the core of a liquid cooled transformer and, more particularly, to apparatus for confining liquid cooling within the core of a liquid cooled transformer.
In design of an electrical transformer, it is generally desirable to optimize space utilization. That is, a transformer having a predetermined rating should be as small as physically possible, consistent with accepted electrical design principles. A major consideration, and a factor that often prohibits reducing the size of the transformer below a predetermined limit, is the amount of heat generated in the transformer during operation. Several schemes have been used to augment cooling of transformers over that available by using the ambient environment. One such technique employs a gas cooled transformer, such as is disclosed in U.S. Pat. No. 4,477,767 - Cotzas, assigned to the present assignee, wherein the transformer is disposed in a cooling dome of a large dynamoelectric machine for beneficially using the cooling fluid, typically hydrogen gas, used to cool the rotor of the dynamoelectric machine. However, gas cooled transformers typically require internal passageways and vents for permitting the coolant gas to flow therethrough and directly to contact the laminations of the transformer core. (The core of a transformer is typically fabricated from a plurality of stacked laminations in order to reduce eddy currents and heat resulting therefrom. The laminations are generally tightly compressed together during fabrication to ensure adequate surface contact with adjacent laminations and to minimize overall size). These passageways, or ducts, increase the overall physical size of the transformer over that possible using a more efficient, (i.e. one having a higher thermal conductivity) heat exchange medium, such as a liquid like water, and/or require space which could beneficially be used to provide additional laminations for the transformer core, thereby increasing the rating of the transformer within the same sized outer housing.
Another technique for cooling transformers uses a liquid, such as water, or preferably deionized or distilled water. In certain applications, it is desirable that the water not directly contact the laminations of the transformer core. In order to contain the water within the transformer without having the water directly contact the core laminations, yet still be in heat flow communication with the laminations, a chamber, which may be disposed between core laminations and in heat flow communication therewith, is provided. To minimize the size of the chamber and to optimize heat flow between the laminations of the transformer core and liquid within the chamber, it is desirable to minimize the thickness of the chamber walls. However, during fabrication of the transformer core, it is necessary that the laminations, having chambers predeterminedly spaced therebetween, be compressed in order to minimize the spacing between individual laminations and the overall size of the core. Forces involved in such compression tend to crush the side walls of the chamber, thus reducing the volume for liquid flow through the chamber and thereby reducing the cooling effectiveness of the chamber. In addition, in order to ensure tightly packed core laminations, especially during operation of the transformer, it would be desirable to utilize pressure available from the liquid coolant to beneficially exert compressive force on the laminations.
During operation, magnetostrictive forces, caused in part by eddy currents induced in laminations of the core, act to separate and vibrate the laminations. It is desirable to maintain the tightness and compactness of core laminations achieved during core assembly since loose laminations tend to vibrate. This vibration may cause fretting, wear and excessive or undesirable noise, and looseness may detrimentally reduce heat conduction through the core.
Accordingly, it is an object of the present invention to provide means and method for containing a liquid in heat flow communication with the laminations of a transformer core without succumbing to assembly compressive forces used to fabricate the core.
Another object of the present invention is to provide means and method during operation of the transformer for augmenting compressive forces on laminations of a transformer core, which forces are used to fabricate the core.